The present invention is directed to inspection of transparent containers for commercial variations that affect optical properties of the containers, and more particularly to an apparatus and method for electro-optically measuring thickness of container walls (sidewalls, shoulder, neck, heel and/or bottom).
In the manufacture of transparent containers of glass composition, for example, it has heretofore been proposed to measure the sidewall thickness of the containers in order to detect thin areas that may affect the ability of the containers to withstand pressurization and handling. In one container sidewall thickness gauge commercially employed by applicants"" assignee, a radio frequency electrode is placed near the outer surface of the container wall, and the amplitude of the signal received at a coaxial pick-up electrode is related to container wall thickness. This technique is highly sensitive to the distance between the pick-up electrode and the container wall surface, and the electrode is mounted on a wheel that rides on the container surface in order to control the electrode/surface separation. Mechanical contact with the container and vibration at the probe when the container moves into position cause a high failure rate at the electrode assembly.
U.S. Pat. No. 5,291,271, assigned to the assignee of the present application, discloses an apparatus and method for electro-optically measuring the thickness of a container wall. A light source directs a light beam onto the outer surface of the container at an angle such that a portion of the light beam is reflected from the outer surface, and a portion is refracted into the container wall, reflected from the inner wall surface and then re-emerges from the outer wall surface. A lens system is disposed between a light sensor and the container wall for focusing light energy reflected from the outer and inner wall surfaces onto the sensor. The lens system has an image plane in which the sensor is disposed and an object plane colinear with the light beam. The container is rotated about its central axis, and information processing electronics are responsive to the light energy incident on the sensor for scanning the sensor at increments of container rotation and determining wall thickness of the container between the inner and outer wall surfaces as a function of the separation between the points of incidence of the reflected light energies on the sensor.
It is a general object of the present invention to provide a method and apparatus of the type disclosed in the above-noted patent for measuring wall thickness of transparent containers, which have reduced sensitivity to container position, and which in the preferred embodiments of the invention are adapted to measure wall thickness of containers traveling transversely through an inspection station.
A method of measuring wall thickness of a transparent cylindrical container in accordance with the presently preferred embodiments of the invention includes moving the container transversely through a defined path while simultaneously rotating the container about its axis. A line-shaped light beam is directed onto the wall of the container, with the line-shaped light beam having a long dimension perpendicular to the axis of the container and parallel to the direction of translation of the container. Light energy is directed onto a sensor as reflected from portions of the outer and inner wall surfaces of the container that are perpendicular to the light energy directed onto the container, as viewed from a direction parallel to the container axis, and container wall thickness is measured as a function of separation at the sensor between the light reflected from the outer and inner wall surfaces.
A method of measuring wall thickness of transparent cylindrical containers in accordance with another aspect of the preferred embodiments of the invention includes moving the containers transversely along a defined path and simultaneously rotating the containers about their central axes. Light energy is directed onto each container at an angle to the axis of the container such that a portion of the light energy is reflected from the outer surface of the container wall, and a portion is refracted into the container wall and reflected from the inner wall surface. The portions of the light energy reflected from the outer and inner wall surfaces along a light path co-planer with the incident light energy and with the container axis are directed onto a light sensor. Wall thickness of each container is measured as a function of the separation at the sensor between the light portions reflected from the inner and outer wall surfaces of the container. The sensor is preferably scanned at increments of container translation along the path, and wall thickness is measured at angularly spaced positions around the container corresponding to the increments of container translation along the path. In one embodiment of the invention, the light energy is directed continuously onto each container as the container moves along the path. In another embodiment of the invention, a number of containers are moved and simultaneously rotated along the path, and the light energy is directed onto each of the containers in sequence as the containers are moved and rotated along the path.
Apparatus for measuring sidewall thickness of a container in accordance with the preferred embodiments of the invention includes a conveyor for moving the container transversely of its axis through an inspection station and simultaneously rotating the container about its axis. A light source and an illumination lens system direct onto the sidewall of the container a line-shaped light beam having a long dimension perpendicular to the axis of the container and parallel to the direction of movement of the container through the inspection station. A light sensor and an imaging lens system direct onto the sensor light energy reflected from portions of the outer and inner sidewall surfaces that are perpendicular to the illumination energy as viewed from a direction parallel to the container axis. An information processor is responsive to light energy directed onto the light sensor by the imaging lens system for determining the thickness of the container between the outer and inner sidewall surfaces.
In one embodiment of the invention, the illumination lens system directs the light energy continuously onto each container as it moves through the inspection station. In another embodiment of the invention, the conveyor is constructed to move multiple containers through the inspection station simultaneously and in sequence, and the illumination lens system includes a mirror and an actuator coupled to the mirror to direct the illumination beam onto each container in sequence as the containers move through the inspection station. The information processor is coupled to the actuator for selectively controlling the direction of light energy onto the containers. An encoder is coupled to the conveyor in the preferred embodiments of the invention, and the information processor is coupled to the encoder for scanning the sensor at increments of container motion through the inspection station. The conveyor in the preferred embodiments of the invention comprises a rail and a belt for rolling the container along the rail. The light source is disposed to direct the light energy onto an external surface of the container adjacent to the rail.